The following discussion of the prior art is intended to present the invention in an appropriate technical context, and allows its significance to be properly appreciated. Unless clearly indicated to the contrary, reference to any prior art in this specification should not be construed as an expressed or implied admission that such art is widely known or forms part of common general knowledge in the field.
Clobazam (the Compound (I)) is a psychotropic drug, essentially used for its anticonvulsant effects. The drug is marketed by LUNDBECK LLC under the trade name ONFI® in the form of oral tablets and oral suspension. ONFI is a benzodiazepine indicated for adjunctive treatment of seizures associated with Lennox-Gastaut syndrome (LGS) in patients 2 years of age or older. Clobazam is a 1,5-benzodiazepine, meaning that its diazepine ring has nitrogen atoms at the 1 and 5 positions (instead of the usual 1 and 4). Like other 1,5-benzodiazepines (e.g., arfendazam, lofendazam), it has less affinity for the ω1-allosteric binding site on the GABAA receptor compared to the 1,4-benzodiazepines. It has selective affinity for the ω2 site, where it has agonistic activity. Clobazam binds at a distinct binding site associated with a Cl-ionopore at the GABA-A receptor, increasing the duration of time for which the Cl-ionopore is open.

Clobazam being an important drug for treatment and management of epilepsy and anxiety disorder; a number of processes for its preparation as well as for its intermediates are known in the art.
U.S. Pat. No. 3,984,398 (hereafter US'398) describe a process for the synthesis of Clobazam, which is illustrated below in Scheme-I. In the process, the compound, 5-chloro-2-nitro-N-phenylaniline is reacted with mono alkyl malonate to produce corresponding alkyl 3-((5-chloro-2-nitrophenyl) (phenyl)amino)-3-oxopropanoate which on further reduction converted to diamines compound. The patent US'398 describes the cyclization of alkyl 3-((2-amino-5-chlorophenyl) (phenyl) amino)-3-oxopropanoate in acid medium to obtain 8-chloro-1-phenyl-1H-benzo[b][1,4]diazepine-2,4(3H,5H)-dione (IV). It further describes the reaction of compound-IV with methyl halide to obtain 7-chloro-1-methyl-5-phenyl-1H-benzo[b][1,4]diazepine-2,4(3H,5H)-dione (I)

GB patent no. 1217217 describe a process for the synthesis of Clobazam by the cyclization of 2-amino diphenylamine compound with Malonic acid dihalide and the obtained product compound (IV) is further methylated using methylating agent to obtain compound-1.
Indian patent 259469 (hereafter IN'469) describe a process for the synthesis of Clobazam (I) by the methylation of 8-chloro-1-phenyl-1H-benzo[b][1,4]diazepine-2,4(3H,5H)-dione (IV) using a methylating agent in an biphasic solvent system essentially in the presence of a phase transfer catalyst (PTC).
In addition to the afore discussed patent documents, there are a number of patent documents that describe a process for the preparation of similar compounds and Clobazam derivatives such as published PCT application WO-A-2011/100838, US patent application no. 2003/0149027, GB1274029 and GB1214662, Chemical & pharmaceutical bulletin 38 (3), 728-32 (1990).
It is evident from the discussion of the processes for the preparation of the 8-chloro-1-phenyl-1H-benzo[b][1,4]diazepine-2,4(3H,5H)-dione (IV), and further its conversion into the Clobazam (I), described in the afore cited prior art documents that some of the reported processes primarily provides product with low yield, which involve critical reaction conditions, biphasic reaction solvent system, use of complex reagents, purification using column chromatography and expensive solvents; which renders the process costlier and hence the processes are not industrially feasible.
In view of these drawbacks, there is a need to develop an industrially viable commercial process for the preparation of Clobazam and its intermediates; which is simple, efficient and cost-effective process and provides the desired compounds in improved yield and purity.
Inventors of the present invention have developed an improved process that addresses the problems associated with the processes reported in the prior art. The process of the present invention does not involve use of any toxic and/or costly solvents and reagents. Moreover, the process does not require additional purification steps and critical workup procedure. Accordingly, the present invention provides a process for the preparation of Clobazam and its intermediates, which is simple, efficient, cost effective, environmentally friendly and commercially scalable for large scale operations.